1. Field of the Invention
The present invention relates to a front directional antenna used in a wireless communication system and, more particularly, to an isolation antenna for making transfer characteristics of a back signal zero (0).
2. Description of the Related Art
A method for designing a conventional isolation antenna includes an antennal element arranging step S11, a multi-back shielding step S12, a signal synthesizing step S13, and a back-suppressed pattern outputting step S14, as shown in FIG. 1.
At the antenna element arranging step S11, the antenna elements are arranged at a relatively broad interval (e.g., 0.7 to 1.5 wavelength) to obtain a high directional gain by using a small number of elements, a small number, i.e., 1 or 2 elements 111 are arranged in a horizontal direction and a large number, i.e., 4 to 10 elements are arranged in a vertical direction to reduce a size of the antenna.
The multi-back shielding step S12 is a step for repetitively placing refracted electric wave obstacles 115 and 116 to repetitively weaken receiving intensity of the back signal when the antenna element arranged by the element arranging step S11 receives the back signal.
The signal synthesizing step S13 is a step for synthesizing the signal received by the array element arranged at the element arranging step S11 to a state that the back signal is weakened by the multi-back shielding step.
The back-suppressed pattern outputting step S14 is a step for outputting the synthesized back-suppressed pattern signal to an outside of the antennal so that it can be used by a user.
Here, like a pattern 130 of FIG. 1, a pattern of the output signal has a main beam 131 whose half amplitude has a narrow angle (e.g., 20 degree) due to the refracted electric wave obstacles and a side lobe 132 which has a broad width.
However, the conventional isolation antenna has a problem in that a possible zero point angle 134 of the back signal is limited by size and number of the electric wave obstacles.